The present invention generally relates to electrical machines, such as high speed aerospace generators and motors, and, more particularly, to systems for containment of a high speed generator rotor during a bearing, main rotor or similar failure.
Aircraft systems include various types of rotating electrical machines, such as alternating current (AC) motors and generators of various designs. Generally, the electrical machine includes a rotor and a stator. The rotor is part of a rotating shaft assembly supported by bearings. The stator is part of a static assembly that supports the rotor.
If the machine is operated as a motor, electrical power may be supplied to the stator to develop a rotating electrical field. This rotating electrical field generates a torque in the rotor causing it to rotate. If the machine is operated as a generator, electrical power may be supplied to the rotor to generate a magnetic field. The generated magnetic field rotates as the rotor rotates. This rotating magnetic field induces a voltage across the stator, which supplies electrical power to a load.
For high speed aerospace generators, the operating speed range is typically 7,200 to 30,000 rpm. Potentially large centrifugal forces can be imposed on the rotors of generators operating at such speeds and may result in rotor failure. Additionally, the bearings, which may have very high stiffness and little damping, may fail due to, for example, an unbalanced rotor rotating for prolonged periods of time. During a bearing, main rotor or related failure, excessive axial forces may be produced between the rotor and stator which may lead to uncontained failure of the stator housing.
In U.S. Pat. No. 6,260,667, a rotor containment brake is disclosed. The described rotor containment brake is designed to operate in the delay between the occurrence of bearing failure and the disconnection of the rotor shaft from the driving source. The described brake includes a cylindrical support connected to the housing and extending into a hollow in the anti-drive end of the rotor shaft, a carrier plate connected to the support and extending radially from the support towards the rotor shaft, a screw thread provided on the support, and a threaded plate mounted on the screw thread, the threaded plate extending radially from the support towards the rotor shaft and being spaced from the carrier plate. Rotation of the threaded plate about the support causes the threaded plate to move towards the carrier plate, pressing the plate member of the rotor between the carrier plate and the threaded plate, thereby applying braking force thereto. In the described system, upon a bearing failure, a braking force is applied to the rotor shaft responsive to the bearing failure. Although, the '667 patent addresses rotor containment in the event of bearing failure, it does not address rotor containment in the event of main rotor or other failures that may result in axial forces. Additionally, the described system requires carrier plates and threaded plates that may not be suitable for all applications. Further, manufacturing time and cost may be increased by the installation of carrier plates and threaded plates.
As can be seen, there is a need for containment of the high speed generator rotor during a bearing or main rotor or related failure that results in excessive axial force. There is a need for an improved system to prevent a catastrophic uncontained failure.